As for organic compounds, there are a wider variety of materials and more possibilities to synthesize materials having various functions depending on the molecular design, compared with inorganic compounds. Because of these advantages, photo electronics and electronics each of which uses functional organic materials have been attracting attention in recent years.
As examples of electronic devices using organic compounds as functional organic materials, there are solar cells, light-emitting elements, organic transistors, and the like. These are devices taking advantage of electric properties and optical properties of such organic compounds. In particular, light-emitting elements (electroluminescent (hereinafter, also referred to as “EL”) elements) have been making remarkable development.
Such light-emitting elements have a lot of material-dependant problems for improvement of element characteristics. In order to solve the problems, improvement of an element structure, development of materials, and the like have been carried out.
Research has been made on an element structure of a light-emitting element, in which a hole-transporting layer and/or an electron-transporting layer, and/or the like is/are stacked as well as a light-emitting layer and functions are separated in order to improve element characteristics such as emission efficiency (for example, see Patent Document 1: Japanese Published Patent Application No. 2004-152641).